Arc lamp with movable electrode for arc starting



Jan. 6, 1970 R. E. PAQUETTE '3,488,546

ARC LA'MP WITH MOVABLE ELECTRODE FOR STARTING 2 sheets-sheet 41 Filed Nov. 13, 1967 Jan- 6, 1970 Fe. E. PAQUl-:TTE 3,488,546

ARC LAMP WITH MOVABLE ELECTRODE FOR ARC STARTING 2 Sheets-Sheet 2 Filed NOV. l5, 1967 :um y

m RT OE WU AQ EA WP LE m v: on. -mi N" ATTORNEY United States Patent O 3,488,546 ARC LAMP WITH MOVABLE ELECTRODE FOR ARC STARTING Raymond E. Paquette, Saratoga, Calif., assignor to Pek Labs, Inc., Sunnyvale, Calif., a corporation of California Filed Nov. 13, 1967, Ser. No. 682,279

Int. CL H013 7/36 U.S. Cl. 313-146 Y 10 Claims ABSTRACT THE DISCLOSURE BACKGROUND OF INVENTION ,Field of the invention This invention relates to arc light sources such as arc lamps and methodsfor starting the arc in such arc lamps and, more particularly, to `an arc lamp in which the arc lis started by moving one electrode against the other utilizing high lluid pressure while the electrodes are connected to a source of arc sustaining current.

Description of the prior art Arc light sources are in relatively common use today in applicationsv requiring intense sources of light. For example, such light sources nd application for oscillographic photography, for solar simulation to determine deterioration due to sunlight, for searchlights to mention a very few.

To start such lamps ordinarily requires the initial application of a very high voltage starting pulse which is typically 15,000 volts and which is-supplied by an arc starting or triggenpulse power supply. The starting pulse serves to partially ionizethe gas between the electrodes to flash an are thereacross. Once an arc is started, the power to maintain the same is at low voltage which is typically around 20` volts and which is normally provided by an arc sustaining or main power supply.

' For many applications and in many environments, the requirement of having to provide-a starting pulse power supply is often quite burdensome, both from the point of view of weight and .complex circuitry. This is particularly true since the solefunction of the starting pulse power supply is ytostart the arc. In many applications, where it is desirable to provide intense lightsources, the weight, complexity, size vand expense associated with the requirement ofa starting pulse powerV supply has been found a serious limitation on the use of arc lamps, and many attempts have been made to ind other means of starting such lamps, each of which has certain advantages and disadvantages.- f

For example, arc lamps used-as modulatable light sources for the optical tracking of airborne vehicles make use of an exploding bridgewire which bridges the gap and which, when subjected to arc `sustaining power, is consumed to start the arc. The bridgewire is described in U.S. Letters Patent No. 3,256,459 and U.S. Letters Patent No. 3,274,427 and, while eminently suitable to start the lamp, has the disadvantage of a single use which is of no consequence in missile applications, and would not normally be economically feasible for applications requiring many starts during its useful life.

Another arc starting feature that has been proposed particularly for searchlights is a construction making use of a movable electrode which is electromagnetically moved against the other electrode and then withdrawn. The disadvantage of this type of system is that a large electromagnet and current therefor is required to generate an intense eld to move the electrode. This particular starting feature, however, has a number of disadvantages which include the extremely large weight and bulk of the required magnetic structure, the large current required to energize the magnet, the danger of the electrode losing its magnetic properties as its temperature increases, and, finally, the danger of sticking electrodes unless one electrode is retracted immediately upon application of arc sustaining power.

SUMMARY OF THE INVENTION It is, therefore, a primary object of the present invention to provide an arc lamp construction in which the arc is started, after applying arc sustaining power, by utilizing fluid pressure.

It is another object of the present invention to provide an improved arc lamp construction which is started without the use of a high voltage starting pulse, and without the use of an exploding bridgewire.

It is still another object of the present invention to provide a new and novel method of starting and con structing an arc lamp which offers great advantages where repeated uses, small size, low weight, and high reliability are important factors.

It is still another object of the present invention to provide an arc lamp construction in which one electrode is moved against the other by the application of lluid pressure, and returned to its spaced apart position through pressure within the arc lamp.

Briefly, the arc lamp construction of this invention utilizes a pair of normally spaced apart electrodes, disposed within a sealed envelope, containing a gas under pressure greater than atmospheric pressure. One of the electrodes is supported to be axially movable between a retracted position and a position where it touches the other electrode. The end portion of the movable electrode, opposite the arc end, is normally exposed to atmospheric pressure while the arc end is exposed to the internal lamp pressure. The pressure differential across the end portion of the electrode lirst moves and thereafter maintains the electrode in its retracted position.

To start the arc, the end portion of the movable electrode, normally exposed to atmospheric pressure, is exposed to a high Huid pressure which is in excess to the internal lamp pressure. This causes the movable electrode to move into the touching position until the fiuid pressure is relieved. Application of normal arc lamp sustaining power, coupled with the subsequent retraction of the movable electrode, causes the arc to bridge the gap.

Further objects and advantages of the present invention will become` apparent to those skilled in the art to which the invention pertains as the ensuing description proceeds.

The features of novelty that are considered characteristic of this invention are set forth with particularity in the appended claims. The organization and method of opera tion of the invention itself will best be understood from the following description when read in connection with the accompanying drawing in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view, partly in elevation and partly in cross section, of an arc lamp embodying the present invention;

FIG. 2 is a cross-sectional view of the arc end configuration of a pair of electrodes in accordance with the present invention; and

FIG. 3 is a view, partly in elevation and partly in cross section, of another arc lamp embodying the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings and particularly to FIG. l, there is shown an arc lamp constructed in accordance with this invention comprising an envelope `12 which is typically made out of quartz for well-understood reasons and which denes an interior space 18 which is sealed and which contains a gas under pressure in excess of atmospheric pressure. Also disposed in space 18 are a pair of electrodes 14 and 16 which are spaced apart to define an arc gap 20 therebetween. Electrode 14 may form the cathode and electrode 16 may form the anode of the arc lamp, and both electrodes are normally constructed of a refractory metal such as molybdenum or tungsten. As will be explained in greater detail in connection with the description of FIG. 2, in the preferred embodiment of the present lnvention, the electrodes are constructed of dilierent refractory metals to avoid sticking together.

Electrode 14 is slidingly supported within envelope 12, for displacement along its axis, by a bearing bore 22 in an electrode support member 24. Electrode support member 24 may be formed of quartz or the like, and is rigidly supported by the neck of envelope 12. As will be understood hereinafter, support member 24 does not require to form a seal with envelope 12 since bearing bore 22 is not sealed to electrode 14. As a consequence thereof, the space 26, lying on the opposite side of support member 24 than space 18, is generally at the same pressure as space '18.

There is also provided a tubular member 28 which may, but does not necessarily need, be constructed of a refr-actory metal. Tubular member 28 is sealingly supported within the neck of envelope 12 by a sealing member 30, which may be constructed of quartz, having its outer peripheral surface sealed to the interior surface of envelope 12, and its inner peripheral surface sealed to the outer surface of tubular member 28. Finally, there is provided a bellows 32 which has its end portion 32A sealed to electrode 14 and its end portion 32B sealed to the outer surface of tubular member 28.

Electrode 16 is conventionally sealed into the other neck of envelope 12 as shown, and the particular type of seal forms no part of the present invention. One end of electrode 16 is conventionally connected to a rod 34 with which envelope 12 normally forms a rod seal. An electrical power lead 36 may be connected to rod 34, as shown, to which the positive terminal 36A of the arc lamp current source (not shown) is applied. Similarly, an electrical power lead 38 may be connected to tubular member 28 to which the negative terminal 38A of the arc lamp current source is connected.

The interior space of tubular member 28 is connected to a high pressure lluid source 42 through a lluid line 44 which includes a valve means 46 actuatable by a trigger 48. Some venting means 50 may be connected to line 44 to bleed off the high lluid pressure at a predetermined rate and to protect the system against damage.

In operation, a source of arc power is connected across terminals 36A and 38A which is typically the power necessary to sustain a once established arc. Either simultaneous with or any time after the application of arc sustaining power, trigger 48 is activated to cause high pressure uid from source 42 to enter the interior space of tubular member 28 and pressurize the interior space 33 within bellows 32 with a pressure which exceeds the pressure within space 18. As a consequence of pressurizing space 33, a pressure differential exists across electrode 14 urging the same to move axially in the direction of electrode 16 until the displacement is stopped by touching contact.

As soon as the arc tip of electrode 14 touches thefarc tip of electrode y16, current ow starts and an arc is formed as the electrodes are separated. Application of high lluid pressure is only momentary to move electrode 14 into touching position with electrode 16. After the electrodes touch, the high pressure source is disconnected from line 44, and the fluid pressure in space 33 is allowed to bleed olf thereby reversing the pressure differential across electrode 14 allowing the same to move to its retracted position in which end face 14A of electrode 14 contacts end face 28A of tubular member 28 or some other convenient stop.

It should be noted at this point that the time necessary for returning electrode 14 to its normal retracted position depends on a number of factors including the friction between bearing bore 22 and electrode 14 and the pressure differential across the electrode. Since the speed of retraction should be selected for best arc drawing across the gap, means are provided to control the speed of retraction in the form of vent means 50 which controls the pressure differential across electrode 14. Vent means 50 initially must allow the rapid .build-up of pressure so that electrode 14 is firmly and positively moved into touching position, and thereafter must dissipate the pressure at a rate such that the speed of retraction is optimum for arc drawing. One vent means 50 may take the form of a small opening in line 44 having a diameter such that a certain finite time is required for the pressure within space 33 to return to atmospheric pressure after the application of high pressure. In addition to, or instead of, a vent means in the form of a small opening, a relief valve may be provided which includes a delay to permit maintaining pressure long enough to assure that electrode 14 is moved in the touching position, and thereafter provide venting at a rate commensurate with a described rate of retraction.

Referring now to FIG. 2, there is shown a preferred embodiment of the arc ends of cathode 14 and anode 16 which are particularly suitable for arc lamps which are started by moving one electrode into contact with the other. Cathode 14 is constructed of molybdenum and anode 16 of tungsten. It is generally recognized that placing two electrodes into conductive contact with one another, and applying arc power thereto, will cause a certain amount of sticking if the electrodes are allowed to get very hot and are not rapidly enough withdrawn. This effect is similar to the one used for welding and is extremely undesirable in starting arc lamps. Utilization of dissimilar metals, such as molybdenum for one electrode and tungsten for another electrode, discourages electrode fusion to some extent. Since molybdenum normally has a much shorter lifetime as an arc electrode than tungsten, a tungsten insert is provided in the form of a rod 60 in cathode 14. Further, the end of electrode 14 is shaped in the form of a conoid 62, and a corre sponding or mating conical opening 64 is provided in anode 16. Finally, a cylindrical counter-sink 66 is provided at the apex of opening 64 to clear the tip of insert 60 from touching any part of tungsten anode 16. As cathode 14 and anode 16 come together, conical surface 62 will engage conical surface 64 without sticking because of the dissimilar material, and the actual arc end of tungsten rod 60 remains out of contact with tungsten anode 16.

It is to be understood that a number of modifications can be made within the spirit of this invention. For example, tubular member 28 is herein utilized not only for the purpose of providing a means for applying high tluid pressure to space 33 to move electrode 14, but also to provide a current path to electrode 14 via bellows 32. If desired, arc current carrying ribbons can be attached to bellows 32 or -may otherwise be sealed into the stem of envelope 12 if desired. Further, while ordinarily electrode 16," and 'particularly the configuration shown in FIG. 2, provides a positive and convenient stop for moving electrode 14, it is likewise Within the contemplation of this invention to provide some stopping means such as the end face of bellows lportion 32A contacting support member 24.

Referring now to FIG. 3, there is shown an alternate embodiment of the arc lamp embodying the present invention which includes a numberof features found desirable, from practical considerations,` to effect proper seals. Even though the arc lamp of FIG. 1 illustrates the basic concept of the present invention, the seals there shown are essentially in schematic form to allow for greater clarity in the description of the invention.

Referring now to FIG. 3, there is shown an arc lamp 100 comprising a quartz envelope 102 forming a bulb portion 103, a cathode stern portion 104 and an anode stem portion 117. Cathode stem portion 104 supports a lengthwise movable cathode 105 having one end welded or otherwise alixed to an alignment and backstop pin 106. At the mouth of stem portion 104 there is supported a quartz alignment Iwasher 107 whose inner bore is dimensioned to allow cathode 105 to freelyfslide lengthwise. Also supported within stem portion 104 is a molybdenum sleeve 108 which has sealed to its end portions a pair of molybdenum rings 109 and 110. Ring 109 has an inner bore allowing freely sliding motion `of cathode 105.

Ring 110 has sealed thereto a Kovar cup 111 which in turn is sealed to envelope 102 via a graded seal 112. The inner bore of ring 110 is also sealed to a tubular mem'ber 113 which extends out of stem portion 104 and terminates in a fitting 120. Bellows 114 have opposite ends sealed respectively to ring 110 and the inner shoulder of stop pin 106 thereby completing the sealed structure. There is also provided an anode 116 which is supported in anode stern portion 117 of arc lamp 100 in the usual manner.

The operation of the arc lamp of FIG. 3 is the same as the one described in connection with the arc lamp of FIG. 1, when a source of high pressure is connected to connector tting 120.

There has been described an arc lamp construction in which the cathode is moved under pressure against the anode, and then allowed to return to its retracted position, thereby carrying the arc across ther arc gap. The arc lamp is simple to operate, inexpensive to construct and very reliable, there being no particular requirements irnposed on making the electrode movable which would deleteriously affect either performance, operation or reliability.

What is claimed is:

1. An arc lamp comprising:

a sealed envelope;

a pair of electrodes having arc ends disposed within said envelope, at least one of said electrodes being movable with respect to the other between a normally retracted position in which said ends are spaced apart to define a normal ar-c gap therebetween and a touching position in which said arc ends are in conductive contact;

connecting means for connecting said electrodes to the terminals for a power supply disposed outside said envelope; and

a fluid pressure system including a tubular member sealed to and passing into said envelope and a bellows means sealingly connecting the end of said tubular member to said movable electrode, said bellows means being pressurized through said tubular member to move said movable electrode, said uid pressure system being operable between a first state for urging said movable electrode into said touching position and a second state for urging said electrodes into said retracted position.

2. An arc lamp in accordance with claim 1 in which said bellows means and said tubular member are conductive and in which said connecting means includes said bellows means and said tubular member.

3. An arc lamp in accordance with claim 2 in which at least the portions of said electrodes which are in contact lwhen said electrodes are in said touching position are constructed of different metals to minimize sticking during arc lamp starting.

`4. An arc lamp in accordance with claim 3 in which one of said electrodes is constructed 'of tungsten and the other electrode is constructed of a refractory metal other than tungsten, and in which the arc end of the other-thantungsten electrode is shaped to have a conical end portion and the arc end of the tungsten electrode is shaped to provide a seat mating with said conical end portion, the center of said seat being recessed to prevent the apex of said conical end portion from making direct contact with the tungsten electrode.

5. An arc lamp in accordance with claim 4 in which said other-than-tun-gsten electrode is provided with an axial bore at said conical arc end portion, and in which a tungsten pin having a conical end is disposed within said axial bore to form the operating arc end of said other-than-tungsten electrode, said pin being dimensioned and positioned such that it will not make direct contact with said tungsten electrode when said electrodes are in said touching position.

6. An arc lamp comprising:

a sealed envelope;

a pair of electrodes having arc ends disposed within said envelope at least one of which is movable with respect to the other between a normally retracted position in which said arc ends are spaced apart to define a normal arc gap therebetween and a touching position in which said arc ends are in conductive contact, one of said electrodes being constructed of a first refractory metal and the other electrode being constructed of a different refractory metal, the arc end of said one electrode being shaped to have a generally conical end portion and the arc end of said other electrode being shaped to provide a seat for mating with the conical end portion of said one electrode, the center of said seat being recessed to prevent the apex of said conical end -portion from making direct contact with said other electrode;

connecting means for connecting said electrodes to the terminals of a power supply disposed outside said envelope; and

a fluid pressure system operatively coupled to said lamp for moving said one electrode relative to the other, said uid pressure system being operable between a rst state for urging said one electrode into said touching position and a second state for urging said one electrode into said retracted position.

7. An arc lamp in accordance with claim 6 in which said one electrode is provided with an axial bore at said conical arc end portion and in which a pin formed of a metal other than said rst refractory metal and having a conically shaped end is disposed within said axial bore to form the operating arc end of said one electrode, said pin being dimensioned and positioned Such that it will not make direct contact with said other electrode when said electrodes are in said touching position.

8. An arc lamp in accordance with claim 7 which further includes a tubular member sealed to and passing into said envelope, said member forming a communicating passage between said fluid pressure system and said movable electrode.

9. An arc lamp in accordance with claim 8 which further includes bellows means sealingly connecting said tubular member to said movable electrode.

10. An arc lamp in accordance with claim 9 in which said bellows means and said tubular member are conduc- 3,488,546 7 8 tive and in which said connecting means includes said 3,412,274 11/ 1968 Wolf 313-146 X bellows means and said tubular member.

RAYMOND F. HOSSFELD, Primary Examiner U.S. C1. X.R.

References Cited UNITED STATES PATENTS 5 ,313*148 217 218 1,828,645 10/1931 Cremer 313-148 X 3,065,321 11/1962 Ainsworth 313-146X 

